1. Field of the Invention
The present invention relates to a method and apparatus for the treatment of radioactive wastes. More particularly, the invention relates to a method and apparatus for the treatment of radioactive wastes in which a temporary store tank which is maintained under predetermined atmosphere conditions is adopted for the temporary storage of pellets of a radioactive waste to attenuate the radioactivity of the waste and a binder such as asphalt or plastics is injected to effect solidification, whereby maximum reduction of the volume of the waste can be conveniently attained.
2. Description of the Prior Art
In atomic power plants, radioactive wastes discharged from, for example, a water boiler type reactor, are ordinarily packed and stored in a vessel having a shielding structure designed according to the dose rate of the radioactive wastes so as to reduce the dose thereof. If such radioactive waste is stored in the liquid state containing water, the necessary storage capacity becomes tremendous. Accordingly, the waste is stored after reduction of the volume by evaporation and solidification. It is regulated that the dose rate on the surface of the vessel should be lower than 200 mrem/hr and that the mechanical strength of the vessel should be at least 150 Kg/cm.sup.2.
Conventional methods for the treatment of a radioactive waste water formed with the operation of a water boiler type reactor in an atomic power plant, which is composed mainly of sodium sulfate (Na.sub.2 SO.sub.4), are disclosed in Japanese Patent Publications No. 37518/1978 and No. 37519/79. The first method comprises concentrating a radioactive waste water by a condenser, mixing the concentrate in a drum can with cement to effect solidification and storing the solidified waste in the drum can. The second method comprises concentrating a radioactive waste water by a condenser, mixing the concentrate and asphalt molten by heating, heating the mixture to evaporate water from the waste, packing the resulting mixture of asphalt and sodium sulfate in a drum can and cooling the packed mixture to effect solidification. In each method, as pointed out above, it is regulated that the dose rate on the surface of the drum can should be less than 200 mrem/hr and the mechanical strength (axial compression strength) should be at least 150 Kg/cm.sup.2. In order to satisfy these requirements, the amount of the solidified waste after evaporation of the waste water is 28 Kg per drum can in the first method or 26.4 Kg per drum can in the second method. Furthermore, in the first method, the upper portion of the drum can is substantially occupied by the waste water and it is technically difficult to cover such waste water with cement. These two known methods have the following disadvantage in common. Namely, since a radioactive waste water produced is immediately solidified and stored, it is impossible to increase the pack ratio of the waste in a drum can because of the above-mentioned regulation of the dose rate. Thus, there has not yet been established a practical method or apparatus for treating radioactive wastes with safety.